Supply circuits, in particular switched mode power supplies are well known in the art. Such supply circuits are for example integrated in consumer and non-consumer products. An exemplary application is the powering of light-emitting diodes (LEDs) and/or organic light-emitting diodes (OLEDs), in particular LED/OLED strings used for automotive LED/OLED lighting and in general, battery powered LED/OLED lighting systems.
Supply circuits that are best suited and therefore are preferably used for the above-named applications are in particular Discontinuous Series Resonant Converters with a constant average current output I, in the following denoted as DSRC-I. This type of converter is for example described in WO2008/110978. The functionality of this type of converter is well understood by those skilled in the art and is therefore not explained in more detail. DSRC-I converters provide the advantage of a constant average current output, furthermore, no current sensing and no current control loop is required. Consequently, losses caused by a current sensing are avoided, and the DSRC-I provides a high-efficient, compact and easy design compared to other commonly known series resonant converters.
A disadvantage of the basic DSRC-I converter is that the output voltage has to be lower than the input voltage if no transformer or additional components such as an additional voltage doubler circuit are provided. However, both solutions need space and increase the costs of the circuitry. As an example, an LED backlight of a car, which consists of several LEDs in a series connection will need more than 12 V of the car battery, e.g., 5 LEDs in series require 5×3.3 V=16.5 V. Hence, the DSRC-I causes problems if several LEDs have to be connected in series and only a low supply voltage is available, e.g., in automotive applications.
Battery powered systems often also stack cells in series to achieve a higher output voltage. However, sufficient stacking of cells is not possible in many high voltage applications due to a lack of space.